The textbook Immanuel Kant assigned for his course on Naturrecht was Gottfried Achenwall’s Natural Law. In the Feyerabend transcript of his course (1784), Kant not only explains Achenwall’s text but also criticizes him and expounds his own alternative theory. Since it is not always obvious from the lecture notes whether Kant is explaining Achenwall, criticizing him, or presenting his own theory, one must know the basics about Achenwall’s positions when reading Kant’s Feyerabend lectures. In this essay, we introduce Achenwall and his handbook to readers of Kant’s Feyerabend lectures. We start with some background information and then discuss Achenwall’s position on freedom and obligation, natural law and right, and his theory of property and the state. We end by pointing out a few of the main points of disagreement between Kant and Achenwall that emerge from the Feyerabend lectures.